1. FIeld of the Invention
The present invention relates generally to a pickup cartridge, and more particularly to a pickup cartridge with an improved damper.
2. Description of the Prior Art
Prior art pickup cartridges of the moving magnet type consist of a cantilever with a reproducing stylus at its free end, a rod-shaped magnet magnetized to have N-and S-poles in its longitudinal direction, a sleeve coupling the cantilever to the magnet, and a damper that consists of a disc of synthetic rubber or the like for elastically supporting the cantilever and forming the fulcrum of the vibration of the stylus when the stylus traces a sound groove. The disc is supported by a cylindrical holder.
Such a prior art pickup cartridge is simple in construction and can be mass produced at low cost. Further, it is easy to adjust and has good damping action. THerefore, such pickup cartridges are widely used.
However, in such cartridges the cantilever is apt to be moved forward or backward longitudinally due to the friction between the stylus and the modulated sound groove. Consequently the fulcrum of the cantilever may be shifted easily.
An improved pickup cartridge for eliminating the above defects has been proposed in the art. Its holder is closed at its rear portion and a damper similar to the one just described is provided in front of the closed portion or the innermost end of a cylindrical concave portion. In front of the damper there are arranged a disc-shaped magnet, a cantilever and a sleeve. In addition, a tension sleeve is inserted into the closed portion through the axis thereof to be coupled to the damper for adjusting the front and rear positions of the damper. A tension wire extends through the sleeve to the cantilever which is used to determine the position of the cantilever by adjusting the position of the sleeve.
According to the latter embodiment of the prior art, the stretching condition of the tension wire at adjustment poses a problem. The reason is that the strength of the tension wire affects the damping action of the damper. Also, reasonances of the wire cannot be neglected. In conclusion, the latter prior art cartridges have non-uniform characteristics.